Galileo Didn’t Drop Anything Off The Leaning Tower Of Pisa

“In the sciences the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man.” —Galileo Galilei

In A Nutshell

In the popular story, to demonstrate objects of different mass fall at the same rate, Galileo dropped two spheres of different weights from the top of the Leaning Tower of Pisa. Both hit the ground at the same time. In one fell swoop, the brilliant scientist ended a debate which had raged for two millennia. But the story in all its variations was an invention of Galileo’s student and biographer, Vincenzo Viviani.

The Whole Bushel

We know now objects in a state of free-fall, regardless of their mass, fall at the same rate of acceleration. It wasn’t always so. For much of history, philosophers and scientists assumed Aristotle was correct in theorizing the heavier an object is, the faster it will fall. Aristotle’s work on mechanics was venerated with near religious devotion. But during the 16th century, intellectuals began to seriously challenge the Greek philosopher’s ideas. Naturally, this required experimentation.

In 1586, a young mathematician and engineer dropped two lead balls of different weights from a tower in Italy. He noted both spheres struck the ground seemingly at the exact same moment. The mathematician’s name was Simon Stevin. Rather than the Tower of Pisa, the young man from Flanders utilized a church tower in Delft, Italy for his experiment. Stevin’s experiment preceded dates given for the Galileo story by at least three years. But Simon Stevin was hardly unique. When he conducted his experiment in Delft, Stevin was building on similar tests.

Decades earlier, it’s likely a Venetian scientist, Giovanni Battista Benedetti conducted a similar experiment. And 1,000 years earlier, the little-known John Philoponus performed his own falling bodies experiments with unequal weights. Philoponus was a Byzantine scholar working in the sixth century. He recognized weight could not determine acceleration, though he incorrectly theorized on density’s effect.

But what then of Galileo and the Leaning Tower? Galileo, who taught mathematics at Pisa from 1589 to 1592, did theorize about a similar experiment. However, the experiment Galileo imagined required a tower taller and of different proportions than that at Pisa. Nor is there any evidence in Galileo’s writing to support the performance of such an experiment. This shouldn’t detract from Galileo’s enormous contribution to physics, because Galileo devised a more measurable and repeatable manner of measuring the acceleration of falling bodies. By releasing different balls down ramps Galileo could more easily observe the slower descents rather than trying to eyeball two speeding spheres crashing into the ground. Galileo was working smarter, not harder. Imagine climbing the nearly 300 steps of the Leaning Tower to repeat such an experiment: not the most efficient way to test one’s hypothesis.

Most historians agree the story of Galileo dropping objects from the Leaning Tower to the Pisans’ amazement is apocryphal. Vincenzo Viviani, a former student, made first mention of the story, writing 15 years after Galileo’s death. Viviani, who greatly admired his mentor, created the story, perhaps to more dramatically showcase Galileo’s rebuttal of Aristotle’s long revered theories. Which sounds about right for a biographer who erred on his subject’s birthday and didn’t always accurately describe Galileo’s theories.